High voltage fuse



May 15, 1934.

J. SLEPIAN HIGH VOLTAGE FUSE Filed July 27, 1927 2 Sheets-Sheet lINVEINTOR .7275@,0/7 S/ep/b/v.

AT'TORNEY May 15, 1934 J. sLEPlAN 1,958,9`04

HIGH VOLTAGE FUSE Filed July 27, 1927 2 She-e'S-Sheeb 2 TTQRNEY PatentedMay 15, 1934 HIGH VOLTAGE FUSE Joseph Slepian, Pittsburgh, Pa., assignorto Westinghouse Electric & Manufacturing Company, a ,corporation ofPennsylvania lApplication July 27, 1927, Serial No. 208,686

13 Claims.

My invention relates to electrical circuit interrupting devices andparticularly to fuses for alternating current circuits.

One object of my invention is to provide a circuit interrupter thatshall be applicable to high-voltage alternating current circuits.

Another object of my invention is to provide a structure forinterrupting a circuit that shall conne an electrical arc and cause itto expand predominantly in one direction.

Another object of my invention is to provide a fuse having insulatingexpansion recesses of such length that the arc, for the particularcurrent at which the fuse is rated, shall not quite completely fillthose recesses.

A further object of my invention is to provide a device of the aboveindicated character that shall have a suicient length of arc dissipatingrecesses so that the current shall be interrupted with a minimum arcvoltage, that is to say one which will produce the minimum destructiveeffect upon the insulation.

Heretofore, it has been the practice in the art of designing fuses forhigh-voltage alternating currents, to utilize a liquid medium such asoil, pyrene, carbon tetrachloride and the like, for cooling the arc andfor preventing its re-ignition after the alternating current has passedthrough zero value. Disadvantages are presented in the use of this typeof fuse as the container must be hermetically sealed to prevent theliquid from leaking or evaporating. A further disadvantage inherent in aliquid fuse, is that due to cost and maintenance. A fuse of this typemust necessarily be returned to the manufacturer for renewal and anadditional supply of fuses must be kept on hand to replace those beingrenewed. As the initial cost of installation is high, it follows thatthe maintenancecost may prove burdensome.

The circuit interrupting vstructure of my invention, embodying arestricted medium of air to extinguish the arc, avoids the employment ofa liquid medium, whereby the initial cost and the maintenance thereafteris materially reduced. My invention provides a fuse that may be cheaplymanufactured and that may be renewed in the eld with very little effort,enabling it to be kept in substantially constant operation.

I have found that if the arc resulting from the opening of the circuitis confined between insulating members it may be interrupted and arcre-ignition prevented even more eiectively than in structures employinga liquid medium, or magnetic means. After the arc is thus directedbetween insulating walls that confine the arc to expansion laterally,the conductivity of the arc path therein will be rapidly reduced as thecurrent decreases and the arc will be permanently extinguished as soonas the current passes through zero.

These and other objects of my invention will be made apparent by thefollowing description and its illustration in the accompanying drawings,in which;

Figure 1 is a view, partly in section and partly l in elevation, of afuse embodying my invention;

Fig. 2 is a cross-sectional view of Fig. 1, taken on the section lineII-II;

Fig. 3 is a volt-ampere curve of an arc in air;

Fig. 4 is a volt-ampere curve of an arc that is wholly or partiallyconned by an insulating medium;

Fig. 5 is Ia view, partly in section and partly in elevation, of acircuit breaker embodying my invention, and;

Fig. 6 is a view in cross-section of the conning member taken along theline VI-VI.

My invention comprises, in general, a circuit interrupting structure 1that is provided with an enveloping member having an insulatingcontining recess or recesses of a particular dimension and number,wherein an arc may be drawn and allowed to expand in a mannerhereinafter more fully described.

Two particular forms of my invention are shown in the accompanyingdrawings. In sheet 1 a fuse structure is shown in which the fuse 1 has amain body portion 2 and a threaded ferrule 3 attached to each of itsends. Terminal caps 4 are screwed on the ferrules 3 and are employed asterminals for electrically connecting the fuse 1 to an electric circuit.A fuse element 5 is attached to the interior of the top terminal 4 byclamping one of its ends against a washer 6. The other end of the fuse 5is connected to an electrical conducting element 7 that extends throughslotted insulating members 8 and 9 and that is connected to the lowerterminal 4 by means of a flexible shunt 11 attached thereto by means ofa washer 12. The slotted insulating members 8 and 9 are supported in themain body portion 2 by any method common to the art and is here shownsupported by the cement 10. The lower end of the electric conductingelement 7 cooperates with one end of a coil spring 13 that has its otherend attached to washer l2, the spring 13 being under tension when thefuse 1 is in operating condition.

Owing to the stresses that the fuse member 5 would be subjected to bythe biasing spring 13,

a particular type of fuse member should be employed, one that will notbe distorted by repeated heating due to small overloads. The typeillustrated in the drawings which does not constitute any part of mypresent invention, is a preferred form consisting of a low meltingsolder uniting fusible material of a higher melting point. The fusiblematerial has a reduced section for rupturing on short circuit currentswhile the low melting solder will release the fuse member whensufficient heat produced by an overload current is present. 'Ihisconstruction prevents the heating of the fusible material by currentsjust less than suffice to melt it, from producing distortion undertension of the coil spring 13.

The insulating members 8 and 9 that are supported in the main bodyportion 2 by the cement 10, have deep parallel slots 15 of approximatelythe same width, disposed perpendicular to a central slot 16 betweentheir adjacent faces.

It was found by experiment that as the distanceA between the insulatingmembers 8 and 9, or as the width of the slots 15 and 16 was reduced, thecircuit Voltage which could be interrupted per inch length of the slotswas materially increased. Further experiments disclosed that for arcsbetween copper terminals in insulating slots il.; inch wide with acurrent of 550 amperes at -60 cycle, circuit voltages of 1400 volts perinch of arc would be successfully interrupted. It was with slots ofapproximately this width that successful experiments were carried out.

Assuming the fuse to be connected in a high voltage alternating currentcircuit, .upon a shortcircuit occurring therein, the fuse element 5.willbe ruptured at its reduced section 14, the electrical conducting element7 will be released. Due to the tension in the coil spring 13, theelement 7 is drawn through the slot 16, drawing with it the arc formedin the top chamber of the fuse.

The arc so drawn will fill a greater or less portion of the slots 15 or16, depending on,the magnitude of the current at any instant, but thearc Voltage will be a constant, namely that minimum voltage at which anarc can be maintained in a slot of the width of 15 or 16. If the currentin the arc increases, the arc will merely spread and occupy a largerportion of the slots 15, 16 without an increase vof arc voltage,provided the current is not so great that the slots 15, 16 do becomecompletely lled with the arc. Y

As the arc current diminishes, the portion of the slots occupied bythearc also diminishes, but of course there is a lag in this because of thetime taken for ions to recombine. However, this lag will be small,because of the rapid recombination of ions on the walls of the slots,and because of the close proximity of every part of the arc to slotwall.

I After the arc current passes through zero, if the arc does notre-ignite, the voltage across the I fuse will rise to the open circuitvalue in a very short time depending on the nature of the circuit. Forordinary commercial circuits, this time is between 1/50,000 and1/250,000 seconds. During this time, the ions in the space aredisappearing mostly by recombination. If the ions disappear suicientlyrapidly, the rapidly rising voltage will not be able to break the spacedown, and the arc will not re-ignite. But if the ions do not disappearquickly enough, the rapidly rising voltage will break down the space andcause the arc to re-ignite. By making the slots narrow, all parts ofthearc are brought close tp the walls and recombination of the ions is`thereby hastened.

`\length of arc, the lateral extent of the slots is determined by thecondition that if the arc is confined in too small a space, the energyinput into the arc becomes so great as to destroy the insulating walls.By permitting the arc to expand laterally not only is the energy inputinto the arc reduced, but the energy input per inch of slot wall is alsogreatly reduced, so that the insulation is able to withstand the periodof arcing. This will be made clearer by considering the properties offree and combined arcs.

It is well known from past experiments that the voltage required tomaintain an unrestricted arc in air decreases as the current increasesand vice-versa. The curve representing this relation is shown. in Fig.3. If, however, the arc is entirely conned as in a straight circularhole, the curve takes a dilerent form, as shown in Fig. 4, in which thevoltage from the time of the confinement of the arc will have anascending value as the current further increases. This is illustrated bycurve CED of the figure in which an increase of the current to theposition J corresponds to a decrease in voltage to F. The point Ecorresponds to a condition where the arc completely fills the hole inthe insulating medium; and as it can expand no further with an increaseof current, the voltage curve will -ascend as Shown by theportion of thecurve ED.

Further experiments disclose that an arc, confined as regards expansionin one direction, between two insulating members, will expand laterallytherebetween, the length ofA the lateral expansion being a function ofthe current and the distance between the adjoining insulating members.The arc voltage during such expansion remains constant in Value aspreviously stated, since an increase of current merely tends to expandthe arc further between the insulating members.

When the current has increased to a value J, as shown in Fig. 4, the arcbeing conned between the opposite walls of the insulating medium and thevoltage will have decreased from C to E, a further increase in currentwill cause the arc to expand laterally, the arc voltage remainingconstant as shown by dotted lines EF.

The constant arc voltage isa function of the distance between theadjacent insulating members, since an increase of current causes adecrease in voltage until such time as the arc 13@ makes contact withthe adjacent walls. This corresponds to an arc voltage at the lowestpoint of the curve, as at E in Fig. 4. If the distance between theadjoining insulating members is decreased, the constant arc voltageaforesaid will be greater, as illustrated by the dotted line GSH of thecurve CGSH. It therefore follows that a higher constant arc voltage willbe obtained if the distance between the adjacent insulating 14@confining members is reduced.

In the aforesaid example, the current had reached a value J at the timeits lateral expansion was limited on one side by the walls of the slot16, resulting in a constant arc voltage EF. l45 If, however, thedistance between. the insulating confining members is reduced, the arcwill be confined before the current reaches a value J, as at a positionK, resulting in a constant arc Voltage GH of higher value than the arcvoltage EF obtained when the current increased to a greater value J. l

Experiments disclosed that a distance of 1A" between the insulatingconfining members will result in a constant arc voltage of approximately50 volts per inch length of arc. If, however, the distance between theinsulating conining members is reduced to fg" theresulting constant arcVoltage will have a value of about 75 volts per inch.

If the confining space is limited so that expansion of the arc islimited in all directions at some value of current, a further increaseof current results in a corresponding increase of the arc voltage whichthereupon increases rapidly with each increase of current. It istherefore necessary to provide a confining space of cross-sectional areasuited for the particular currents it is intended to interrupt toprevent the arc voltage, and with it the arc-energy, from increasing toso excessive an amount as would destroy the confining insulating memberand result in the restriking of the arc. This is also shown in Fig. 4 bythe curves QR and ST, which show the arc voltage rapidly increasing fromthe constant values EQ and GS to R and T, respectively, when the arc hasexpanded suiciently to fill the entire section of the slot.

It thereforefollows that the time for accomplishing the extinguishing ofan arc in accordance with my invention will be a half-cycle or less,since the current reaches zero value twice during the period of onecycle.

The aforegoing description applies to any arc conned between insulatingwalls and free to expand in one direction only. Sheet 2 of the drawingsillustrates another embodiment of my invention in which a circuitinterrupter 17 comprises the usual operating magnet and separablecontacts but instead of the arc-chute heretofore employed in the art,the drawings show insulating members forming a narrow slot forextinguishing the arc. This structure will now be more fully described.

The contacter 17 is mounted on an insulating base member 18 andcomprises an iron core 19, coil 20 and armature 21, the armature 21being supported on amovable-arm 22 by a pin 23. The

movable arm 22 is hingedly supported at its lower end to the iron core19 by a pin 24, its upper end being the means for supporting a movingcontact member 25. A stationary contact member 26 is rigidly secured tothe base member 18 by a member 27 which is of conducting material andwhich is in circuit with the apparatus to be controlled. The otherportion of the circuit illustrated by a conducting lead 28 is shownconnected to the moving contact member 25. Current flow in a circuitconnected with the conducting leads 28 and 29 is controlled by theposition of the contact members 25 and 26.

A supporting member 30 is the means of support for two confining members31 composed of soapstone or other arc resisting insulating material. Theconfining members 31 as shown in Fig. 6, are mounted near each other toform a narrow groove 32 constituting av deionizing structurey of a typeheretofore mentioned. The lower portion of the groove 32 tapers to agreater width to form a chamber for the reception of the arc. Thelateral expansion of the arc is limited by the side wall of the members3l, while the longitudinal expansion is limited by the conductor members33 and 34 which are separated by a distance corresponding to the ratingof the circuit breaker. A iiexible current carrying shunt 35 is employedto electrically connect the moving contact member to the conductingmember 34. The other conducting member 33 is permanently connected tothe stationary contact member 26. When the contacts are open, a circuitis thus formed through the plates33 and 34 and the arc resulting fromthe opening of the contacts. vAuxiliary contact members 36 and 37 of anytype may be provided and these may be open or closed in either positionsof the contact member and may be employed to operate any auxiliarycircuit.

Assuming the contactor 17 to be in the closed position with voltageapplied to the potential coil 20 to hold the armature close to the ironcore 19, the contact members 25 and 26 will be in contact, completingthe circuit through the conducting leads 28 and 29. When the voltage isreduced or cut off from the coil 20, the armature 21 will be releasedand the movable arm 22 will turn in a counter clockwise direction, dueto gravity, about the pin 24, carrying the movable contact member 25away from the stationary contact 26. The arc`drawn upon separation ofthe Contact members will move upward passing from the contact members 25and 26'onto the plates 33 and 34 into the narrow space between themember 32 and will then be extinguished as a result of the deionizingeffect of the narrow slot 32 in a manner heretofore ldescribed.

I have therefore provided a structure that is capable of interruptinghigh voltage alternating current circuits without the use of a liquidmedium or magnetic structure as heretofore has been the practice. Y

My invention de-ionizes the conducting path of the arc when the value ofthe current decreases in such manner that the voltage gradient requiredto restrike the arc between the arcing terminals will be greater thanthe line voltage at all times after the current has reached zero valueand the arc, after being extinguished, will fail to restrike when thevoltage is re-established.

The construction of my invention is simple, resulting in an interruptingdevice having a minimum cost. In the form of a high voltage fuse, myinvention is further useful, in that it can be renewed in the eld by themere application of a new fuse element, while heretofore, it has beennecessary to return the entire fuse to the manufacturer and have itagain renewed and hermetically sealed before it could be again appliedto a high Voltage electric circuit. It is therefore apparent that mytype of fuse is much more economical, both in the saving of time andmoney, than any fuse heretofore invented of the aforesaid type.

As the structure herein desribed and illustrated is only specicembodiments of my invention. I do not intend it 'to be limited to fuseor circuit breaker structures, for the inventionv is applicable tocircuit interrupting devices of many other forms. I further do not wishto be restricted to the speciiic arrangement of parts herein set forth,as various modifications thereof may be effected without departing fromthe spirit and scope of my invention. I desire, therefore, thatonly-such limitations shall be imposed as are indicated in the appendedclaims.

v I claim as my invention:

1. The combination in a fuse structure having a casing and endterminals, of an insulating member disposed within the casing andprovided with a plurality of narrow connected slots, a fuse elementadjacent one of the slots, and biasing means passing through the saidslot attached to the fuse whereby upon the rupturing of the fuse elementthe arc incident thereto will` be drawn into the one slot from which itmay expand into the other slots.

2. The combination in a fuse structure having a casing and endterminals, of an insulating member disposed within the casing andprovided with a plurality of slots approximately one-six-4 teenth of aninch in width, a fuse element and a biased conductor passing throughoneof the slots, whereby upon the rupturing of the fuse element the arcincident thereto will be drawn into one of the slots from which it mayexpand into the other slots. l

3.' The combination in a fuse structure having a casing and endterminals, of an insulating member disposed within the casing andprovided with a plurality of slots of uniform width, a fuse element anda biased conductor passing through one of the slots, whereby upon therupturing of the fuse element the arc incident thereto will be drawninto the one slot from which it may expand into the other slots.

4. The combination in a fuse structure comprising a casing and endterminals, of a pair of semicircular members of insulating materialhaving a plurality of deep narrow slots disposed in the faces thereofand assembled to form a cylinder, the said faces abutting each other toform an additional slot, a spring biased conducting element passingthrough the said additional slot, and a fuse element disposed on theupper terminal above the said cylinder and engaging an end of the springbiased conducting element, whereby upon the rupturing of the fuseelement, the arc incident thereto will be drawn into the said additionalslot by the spring biased conducting element and may expand into thenarrow slots adjacent thereto.

5. The combination in a fuse structure comprising a casing and endterminals, of a pair of semicircular members of insulating materialhaving aplurality of deep narrow slots disposed lengthwise in the facesthereof assembled to form a cylinder, the said faces engaging each otherto form an additional slot, a -fuse element associated with the saidadditional slot and electrically connected toan end terminal.

6. An alternating current fuse structure having a plurality ofinter-communicating narrow insulated slots, a fuse element disposedadjacent one of the slots and means for biasing the fuse element,whereby the arc incident to the rupturing of the fuse element will bedrawn into the said slot where it may expand into the other said slotsand be extinguished when the current passes through zero value.

7. In a fuse structure, insulating means dening a narrow slot having alateral dimension several times its width, a fuse element adjacent saidslot and in parallel relation therewith, and

means for causing the arc incident to the rupturing of said fuse elementto play in said slotand expand therein between said insulating means.

8. In a fuse structure, insulating members having a narrow slot therein,a fuse element arranged to cause an arc in said slot, said slot having alateral dimension several times its width and being arranged to closelyoonne the arc throughout its length in one direction and to allow it toexpand laterally in the other direction.

9. In a fuse structure, insulating members having a narrow deep slottherein, a conducting member having a fusible portion, extending throughsaid slot and parallel therewith for drawing an arc in said slot, thelateral dimension of said slot being Lseveral times its width so thatthe arc is restricted in one direction and allowed to expand laterallyin the other direction.

10. A circuit interrupting structure having slotted insulating means forconning the expansion of an arc throughout its length in one directionand permitting it to expand in the other, said slot being less thanone-fourth of an inch in Width and having a lateral dimension severaltimes its width and means movable in said slot for initially drawing thearc therein.

1l. In a circuit interrupter, separable meansfor drawing an arc, andinsulating means for extinguishing the arc having side walls defining aslot having a lateral dimension several times its width and said widthbeing so narrow as to restrict the width of the arc and cause it toexpand laterally, and said slot between said side walls being positionedbetween said means for drawing the arc when in separated position.

l2. In a circuit interrupter, separable means for drawing an arc, and'insulating means for extinguishing the aro having side walls dening aslot having a lateral dimension several times its width and said widthbeing so narrow as to restrict the width of the arc and cause it toexpand laterally, said separable means for drawing the arc being movablebetween the side walls of said slot for initially drawing the arctherebetween.

i3. In a circuit interrupter, separable -means for drawing an arc, andinsulating means for extinguishing the arc having side walls defining aslot having a lateral dimension several times lts width and said widthbeing so narrow as to restrict the width of the arc and cause it toexpand laterally, said separable means for drawing the arc being movablebetween the side walls of said slot for initiallyY drawing the arctherebetween and means outside of said slot biasing said separable meansfor drawing the arc to separated position and means causing theseparation of said means for drawing the arc upon the occurrence of apredetermined current.

JOSEPH SLEPIAN.

